INTERACTION SPECIFICITY OF THE BIOCONTROL AGENT SPOROTHRIX FLOCCULOSA- A VIDEO MICROSCOPY STUDY

Sporothrix flocculosa, a biocontrol agent reported to act by antibiosi s, had a differential effect against four target fungi, based on video microscopy records of the interactions. Two of the fungi, Botrytis ci nerea and Cladosporium cucumerinum, were very susceptible and reacted ahead of the advancing colony of S. flocculosa. Typical reactions incl uded retraction of the plasmalemma, aggregation of the cytoplasm, and cell death. When S. flocculosa was inoculated directly onto a colony o f B. cinerea, conidia of the biocontrol agent developed toward the pat hogen, and the hyphae of B. cinerea ceased cytoplasmic activity and be came highly vacuolated within 8 h. Individual conidia of S. flocculosa produced several germ tubes, but did not attack live, necrotic, or de ad hyphae of the pathogen. The other two tested fungi, Fusarium oxyspo rum f. sp. radicis-lycopersici and Idriella bolleyi, were unaffected b y the presence of S. flocculosa. These results correlated with previou s observations that C. cucumerinum and F. oxysporum f. sp. radicis-lyc opersici were, respectively, sensitive and tolerant against purified t oxins of S. flocculosa. This indicates that the host range of S. flocc ulosa is dictated by host sensitivity to its toxins.